Spatio-Temporal Analysis of Tuberculosis in Hamadan Province, West of Iran, from 1992 to 2013.

Background: Tuberculosis (TB) despite being preventive and treatable still imposes a huge burden of morbidity and mortality in developing and developed countries. We aimed to investigate the spatial and geographical distribution of TB in Hamadan province during 1992–2013. Materials and Methods: This cross-sectional study was performed in Hamadan province, West of Iran using the surveillance database. We examined the trend for incidence rates of all TB forms including Smear Positive Pulmonary TB (SPPT), Smear Negative Pulmonary TB (SNPT) and Extra pulmonary TB (EPT) per 100,000 populations. Poisson regression model was used to estimate the standardized rates for incidence rate of all types of TB per each county. Results: In this study 3,602 TB patients including 1,359 SPPT, 987 SNPT, and 1,256 EPT were included during 1992–2013. Trend of all types of TB decreased from 1992 to 2013. The Average Annual Percent change (AAPC) for all types of TB was significantly (P<0.05) decreased, AAPC= −6.4 (95% CIs: −10.7, −1.9). Among SPPT, SNPT, and EPT incidence rates, the maximum change was related to SNPT (−11.6; 95% CIs: −24.2, 3), while it was −1.4 (−8.7, 6.4) for SPPT and −5.8 (−11.4, 0.1) for EPT. Conclusion: Our results showed that the incidence of TB in Hamadan province during a 22-year period has decreased 6.4% on average, somehow higher than the national average. Furthermore, our study showed that the risk of extra-pulmonary occurrence in western parts of the province is higher than others parts.


INTRODUCTION
Simultaneously, there were more than 10.4 million new cases and 1.8 million deaths attributable to TB (4). Iran is neighboring with the three most TB prevalent countries, namely Pakistan, Afghanistan, and Iraq (4). Nevertheless, the trend of TB has been decreasing since the introduction of Directly Observed Treatment, Short-course (DOTS) strategy in the country (5). According to the same year`s report of WHO, the incidence of TB in Iran decreased from 18.4 in 2000 to 13 in 2015 (per 100,000 population) (6). The global epidemiology of TB is well-studied; however, some concerns stemmed from the fact that the global distribution of TB is asymmetric. In other words, it is influenced by a pile of geographical (e.g. access to health care) and environmental (population socio-economic status, density, poverty, and health literacy level) factors (7)(8)(9). Therefore, determination of the hotspots and high-risk areas in order to identify the most important causes of TB in different parts of the world has become a milestone in prevention strategies. This approach is quite well known as "spatial Epidemiology". It utilizes GIS (Geographic Information System) software and other spatial statistics to describe the role of environmental and geographical factors in the disease occurrence, and to select the factors that have the most impact on allocation of preventive and curative resources (10,11). Furthermore, describing the trend of the disease over time may provide proper information on the effectiveness of various preventive and therapeutic healthcare services, while it can also predict the future rate and frequency of the disease for policy health makers. An investigation of the trend of TB in Iran conducted by Arsang et al. showed that since 1992 the trend has decreased due to the improved sanitation and health indices. The authors also reported the lack of non-linear models to address non-linear trends of the disease in the country as the main challenge of their study (12).  (13). Given the importance of the temporal trend of TB and application of non-linear models to determine the hotspots, the present study investigated the spatial and geographical distribution of TB in Hamadan province during 1992-2013.

Study area
This cross-sectional study was performed in Hamadan province, West of Iran using the surveillance database. All provincial registered TB patients from 1992 to 2013 were included in the study.

Data source
We examined the trend for incidence rates of all TB forms including Smear Positive Pulmonary TB (SPPT), Smear Negative Pulmonary TB (SNPT) and extra pulmonary TB (EPT) per 100,000 populations. TB cases were defined according to the WHO and national TB guideline in Iran (14). Expatriate patients such as Afghans, non-native patients, and imported cases were excluded from the study.

Temporal pattern
Due to non-constant trend for types of TB over this time period, segmented analysis was used. This model assumption is that changes in the rates are constant over each time segment called change points, but varies with other time segments (15). In this study the trend, Annual

Spatial pattern
Using Poisson model, standardized rates were estimated for incidence rate of all types of TB per county.
In a given population , observed number of events depends on (1)  For SNPT higher rate ratio was related to Famenin and Kabudarahang counties, respectively. In the case of EPT, the higher rate ratio was related to Hamadan city ( Figure 1).

CONCLUSION
Our results showed that the incidence of TB in Hamadan province during a 22-year period has decreased 6.4% on average, somehow higher than the national average. Furthermore, our study showed that the risk of extra-pulmonary occurrence in western parts of the province is higher than others, while this type of the disease in Hamadan city as a canon of political and geographical area in the country has significant implications.